Over the years wireless systems have significantly increased in number and applications. Voice and data transmission lead the current usage of wireless devices. New applications are creating more wireless demand, and higher bandwidth requirements are putting pressure on the currently used wireless systems and radio spectrum allocations. Data rates are approaching and will be exceeding the 1 gigabit per second (1 Gb/s) speed point. Gigabit LAN and high definition digital television are examples of applications that will demand very high bandwidth wireless solutions.
By making use of higher frequency radio waves, it becomes practical to create wireless systems with higher operating bandwidths. As an example, the unlicensed wireless LAN spectrum allocated in the U.S. in the 2.4 GHz band extends from 2.4000 to 2.4835 GHz, resulting in an operating maximum bandwidth of 83.5 MHz. The U.S. 60 GHz unlicensed spectrum extends from 57 GHz to 64 GHz, resulting in a maximum bandwidth of 7 GHz (greater than 80 times the bandwidth at 2.4 GHz). Hence the ability to solve greater bandwidth demand is found by exploiting the millimeter wave frequency bands—generally considered those frequencies above 30 GHz.
Designing circuitry for millimeter wave transmitters and receivers requires scaling down the physical size of the electrical interconnect techniques that work fine at the lower frequencies but degrade as the operating frequency increases (and wavelength decreases). The most cost effective technology for integrating transmitter and receiver circuitry is the integrated circuit (IC) based on a semiconductor process. Current semiconductor process technologies have now enabled the ability to create ICs that operate in the millimeter wave regions up through 100 GHz.
Since the physical size of electrical interconnects inside of an IC are extremely small (on the order of 10−6 meters, or microns), it is feasible for the IC to operate at frequencies in the 30 to 100 GHz range (with wavelengths on the order of 10−3 meters, or millimeters). The problem that immediately presents itself is how to get the millimeter wave energy to and from the IC without appreciable attenuation and loss. The standard method for interconnecting an IC to its outside environment is wire bonding. Small wires are bonded to terminal pads on the IC with the other end of the wires bonded to a pad within the IC package, which in turn are connected to the outside pin on the package typically through a printed circuit trace. The electrical properties of the wire bond, pads and the printed circuit trace (inherent inductance and capacitance) creates appreciable attenuation and unwanted radiation (all adding up to unacceptable losses) at millimeter wave frequencies.
What is needed is a system and method to interconnect a millimeter wave antenna to the integrated circuit without incurring losses through legacy low frequency connections in an efficient and inexpensive integrated antenna and chip package.